Scoring the Vault

A gymnast received these scores from five judges in the state competition. Her score for each event is found by computing the average (mean) after the high and low scores are thrown out. Find a if the vault was her worst event. Find a if the vault was her best event.

Floor: a, 9.3, 8.1, 8.9, 9.5
Bars: 7.6, 8.2, 8.5, 8.2, 8.9
Vault: 9.5, 8.9, 9.4, a, a
Beam: 8.4, 8.5, 8.4, a, 8.7

(Source: Mathematics Teaching in the Middle School, Mar-Apr 1996)